Fluid loss control (FLC) pills are commonly used in hydrocarbon recovery operations after every gravel pack and frac-pack (fracturing with a gravel pack) to reduce the amount of completion brine entering the treated production zone. Present FLC pill technology uses hydratable polymer-based viscous fluids. In some cases the viscous polymeric fluids may contain graded particulates such as ulexite, calcium carbonate, and the like as bridging or plugging agents. The FLC pills are typically removed (cleaned-up) from the wellbore by acids, oxidizers, enzymes, and other like degradation agents.
However, complete FLC pill removal that leaves very little to no formation, gravel, and/or proppant pack damage is often not achieved. Polymeric-based FLC pills often contain 3.0 to 5.0 lbs of polymer per gallon of LCM pill (about 0.4 to about 0.6 kg/liter), which is a significant amount of polymer to remove. A typical polymeric gelling agent may be a solvatable polysaccharide, which may or may not be crosslinked. In most cases, unbroken polymer and residue of broken polymer is left within the wellbore region which causes impaired production of the hydrocarbon bearing zone.
Viscoelastic surfactant (VES) fluids are known to be much less damaging to formations, gravel and proppant packs compared to polymeric fluids but are generally considered inadequate in performance for use as FLC pills. For example, many VES fluids readily leak into porous media with permeabilities greater that about 1 Darcy. For this reason attempts have been made to use graded size particles of polymer and/or inorganic compounds to aid in plugging the porous media to prevent completion brine loss to the production zone. However, the added polymer and/or other particulates are typically counterproductive in that they will also be difficult to remove and will cause formation and other near wellbore permeability damage.
It would be desirable if a new and robust VES fluid loss control pill could be devised that would inhibit or control fluid loss in a well, but that did not require the use of polymers or other materials that are difficult to remove or may cause near wellbore permeability damage.